JPH07131964A - Brushless motor - Google Patents

Abstract

PURPOSE:To provide a brushless motor having a low noise level in cases of both its start and stationary rotation. CONSTITUTION:An FG pattern 3 is connected with a phase comparing circuit 6 via an FG amplifier 4 and a zero-crossing detector 5. The phase comparing circuit 6 decides whether the rotation of a brushless motor reaches its stationary one or not, and sends coil switching signals to a circuit 9 for processing position sensing signals. Based on the decision result, the phase comparing circuit 6 sends the coil switching signal whereby the motor is driven with six coils when the motor is started, and it sends the coil switching signal whereby the number of the coils which carry currents is switched from six to three when the rotation of the motor reaches its stationary one. The circuit 9 for processing position sensing signals sends signals to a current driver 14 via an amplitude controlling circuit 13. The current driver 14 feeds currents to the coils and drives them.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a brushless motor used in an optical scanner of a laser beam printer or the like for supplying a current to a plurality of coils and rotating a magnet by a magnetic field generated in each coil. .

[0002]

2. Description of the Related Art Conventionally, a brushless motor used for an optical scanner of a laser beam printer or the like reverses the magnetic force generated in the coil by switching the direction of the current supplied to the coil, and the The magnet is rotated by repeating the switching of the attractive force and the repulsive force generated during.

In such a brushless motor,
For example, there are a three-coil motor using three coils and a six-coil motor using six coils.

According to the experiment for measuring the noise level of the brushless motor conducted by the inventor of the present invention, the three-coil motor had a noise level of 53 dB at start-up and 42.5 dB at steady rotation. On the other hand, the noise level of the 6-coil motor was 51 dB at startup and 46 dB at steady rotation.

[0005]

In the above-mentioned conventional brushless motor, the noise level at the time of starting is higher in the 3-coil motor than in the 6-coil motor, and the noise level at the steady rotation is 3 in the 6-coil motor. It will be higher than the coil motor.

[0006] Therefore, an object of the present invention is to provide a brushless motor having a low noise level at the time of starting and steady rotation.

[0007]

In order to solve the above problems, the present invention provides a brushless motor which supplies a current to a plurality of coils and rotates a magnet by a magnetic field generated in each coil. Drive means for supplying a current to the coils of the above number and supplying a current to the coils of a number smaller than the predetermined number during the steady rotation of the motor.

[0008]

The driving means drives the motor by supplying a current to a predetermined number of coils when the motor is started and supplying a current to a number of coils smaller than the predetermined number when the motor is rotating normally.

[0009]

Embodiments of the present invention will be described below with reference to the drawings.

The brushless motor of this embodiment has a magnet portion M and a coil portion A. The magnet portion M is rotatably held on the coil portion A. A rotating shaft O is provided at the center of the magnet portion M. The magnet portion M has a main magnet portion 1 formed around the rotation axis O and an FG magnet portion 2 formed on the outer circumference of the main magnet portion 1 (FIG. 1A).
The main magnet unit 1 is composed of eight S poles and N poles alternately magnetized along the circumferential direction. The FG magnet unit 2 has 12 poles, S poles and N poles, which are alternately magnetized along the circumferential direction. The coil portion A is composed of 6 coils C
1 to C6, Hall elements H1 to H3, and an FG pattern 3 (FIG. 1B). The coils C1 to C6 are arranged along the circumferential direction so as to be located below the main magnet portion 1. The Hall elements H1, H2 and H3 are provided inside the coils C1, C5 and C3, respectively. The FG pattern 3 is provided on the outer circumference of the coils C1 to C6 so as to be located below the FG magnet portion 2. The winding direction and connection of the coils C1 to C6 are shown in FIG.
This is as shown in (c).

Next, the motor drive circuit of this embodiment will be described with reference to the block diagram of FIG.

The FG pattern 3 is connected to the phase comparison circuit 6 via the FG amplifier 4 and the zero cross detector 5. The phase comparison circuit 6 is connected to the external clock 7, the position detection signal processing circuit 9 and the error amplifier 15.
The position detection signal processing circuit 9 is connected to the Hall amplifier 10, the start / stop signal generation unit 11, the thermal protection circuit 12, and the amplitude processing circuit 13. The amplitude control circuit 13 is
It is connected to the position detection signal processing circuit 9, the error amplifier 15 and the current driver 14. The outputs OUT1 to OUT6 of the current driver 14 are connected to the coils C1 to C6, respectively.

In the motor drive circuit described above,
The control operation from the start of the motor to the steady rotation will be described.

The start / stop signal generator 11 outputs a signal to the position detection signal processing circuit 9 when it receives a motor start signal from the outside. In response to this signal, the position detection signal processing circuit 9 sends a signal to the current driver 14 via the amplitude control circuit 13. The current driver 14 supplies a current to the coils C1 to C6 in response to the signal sent from the amplitude control circuit 13. When the motor is started, current is supplied to the six coils C1 to C6. Coil C1
The signal level of the current supplied to C6 is the Hall amplifier 1
It is determined by the signal generated by the position detection signal processing circuit 9 based on the output of the Hall element sent via 0.
The coils C1 to C6 are the output OUT1 of the current driver 14.
A current is supplied from OUT6 to generate a magnetic field. The magnetic field of the coils C1 to C6 causes the magnet section M to rotate. In this way, the motor is started. When the motor is activated, the FG pattern 3 generates an induced electromotive voltage due to the rotation of the FG magnet 2. The induced electromotive voltage generated in the FG pattern 3 is amplified by the FG amplifier 4 and then sent to the zero cross detector 5 to be converted into a logic signal. This logic signal is input to the phase comparison circuit 6 and compared with the clock signal from the external clock 7 in the phase comparison circuit 6. As a result of the phase comparison between the logic signal from the zero cross detector 5 and the clock signal from the external clock 7, if these two signals are not synchronized, the motor has not yet reached the steady rotation, so the position detection signal processing circuit 9 The coil switching signal that is sent is output so as to maintain the number of coils to which current is supplied at six.

On the other hand, as a result of phase comparison between the logic signal from the zero cross detector 5 and the clock signal from the external clock 7, the phase comparison circuit 6 judges that the motor has reached the steady rotation if the two signals are synchronized. To do. If the motor has reached steady rotation, the phase comparison circuit 6 sends a coil number switching signal for switching the number of coils to be supplied with current to three to the position detection signal processing circuit 9. In response to the coil number switching signal, the position detection signal processing circuit 9 sets the number of coils to which current is supplied to three and sends a signal to the current driver 14 via the amplitude control circuit 13. Thus, the current driver 14 has coils C1, C3 and C5.
Supply current to the.

The lock signal 8 generated from the phase comparison circuit 6 is set to H level when the motor is started,
When it is detected that the motor is in steady rotation, it is set to L level. The amplitude control circuit 13 controls the amplitude of the current supplied to the coil by the current driver 14 based on the signal sent via the error amplifier 15. Thermal protection circuit 12
Is provided to stop the current flowing through the coils C1 to C6 when the temperature rises due to an abnormality in an IC circuit (not shown).

FIG. 3 is a waveform diagram of each signal at the time of starting the motor of this embodiment. Section (a) shown in FIG.
The states of the current flowing through the coil in (f) are shown in FIGS.

In FIG. 3, first, the Hall elements H1 and H
2 and H3 detect the S-pole, N-pole, and S-pole magnetic poles, respectively (section (a) in FIG. 3). The output of the current driver 14 at this time is that OUT1 is Low (hereinafter referred to as L),
OUT2 is Middle (hereinafter referred to as M), OUT3
Is High (hereinafter referred to as H), and OUT4 is L and OUT
5 becomes M and OUT6 becomes H. Therefore, the coil C3
Current from C6 to C1 and from C6 to C4
3 and C6 act as south poles, and coils C1 and C4 are N
It works as a pole (Fig. 4 (a)).

Next, when the magnetic poles detected by the Hall elements H1 and H2 do not change and the magnetic pole detected by H3 changes from the S pole to the N pole, the output of the current driver 14 is OUT1 is L, OUT2 is H, and OUT3 is M, OUT4 is L, OU
T5 becomes H and OUT6 becomes M. Therefore, the coil C
Current flows from 5 to C1 and from C2 to C4, the coils C5 and C2 function as south poles, and the coils C1 and C4 function as north poles (FIG. 4 (b)). Subsequent operations are the same as the above-mentioned operations, and will be omitted.

As described above, the Hall elements H1 and H2
, And currents are supplied to the coils C1 to C6 according to the positions of the magnetic poles of the main magnet portion 1 located above H3, and the motor is started.

FIG. 5 is a waveform diagram of each signal when the motor in this embodiment is in steady rotation. The states of the currents flowing through the coils in the sections (a) to (f) shown in FIG. 5 are shown in FIGS. 6 (a) to (f), respectively.

In FIG. 5, first, the Hall elements H1 and H
2 and H3 detect the magnetic poles of S pole, N pole and S pole, respectively (section (a) in FIG. 5). The output of the current driver 14 at this time is L for OUT1, H for OUT3, and OUT5.
Is M. Therefore, a current flows from the coil C3 to C1, the coil C3 acts as the south pole, and the coil C1 becomes N.
It works as a pole (Fig. 6 (a)).

Next, when the magnetic poles detected by the Hall elements H1 and H2 do not change and the magnetic pole detected by H3 changes from the S pole to the N pole, the output of the current driver 14 is OUT1 is L, OUT3 is M, OUT5 becomes H. Therefore,
A current flows from the coil C5 to C1, the coil C5 functions as an S pole, and the coil C1 functions as an N pole (see FIG. 6).
(B)). Subsequent operations are the same as the above-mentioned operations, and will be omitted.

As described above, the Hall elements H1 and H2
Currents are supplied to the coils C1, C3, and C5 in accordance with the positions of the magnetic poles of the main magnet portion 1 located above H3 and H3, and the steady rotation of the motor is performed.

As described above, in the above embodiment,
The number of coils to be supplied with the current is 6 when the motor is started.
By using a coil and switching to three coils when the motor reaches steady rotation, the noise level can be constantly lowered at the time of starting the motor and during steady rotation.

In the above embodiment, C1 and C3 are rotated at the time of steady rotation.
Current was supplied to the coils of C5 and C5, but C2 and C4
Alternatively, current may be supplied to the coils of C6 and C6.

Although the brushless motor of the above embodiment has six coils, the number of coils provided may be nine. In this case, when starting the motor, 9
The coil may be started, and the number of coils may be switched to 6 when the number of rotations of the motor increases and reaches a predetermined number of rotations. If the number of rotations of the motor reaches steady rotation due to the increase of the number of rotations, the number of coils may be switched to 3 coils. Alternatively, the 9 coils may be directly switched to the 3 coils when the motor starts to be in the steady rotation. Alternatively, a 10-coil motor may be used, and the motor may be driven by 10 coils when the motor is started, and switched to 5 coils at the time of steady rotation.

In the above embodiment, 6 coils are switched to 3 coils after it is detected that the motor has reached the steady rotation. However, the time of switching the coils is from the time of start-up to the steady rotation, for example, of the motor. The number of coils may be switched from 6 coils to 3 coils when the number of rotations reaches 80% to 90% of the normal rotation.

In the above embodiment, the number of coils is switched when the motor reaches the steady rotation speed from the start-up. However, the number of coils is switched when the motor is shifted or when the steady rotation is reached. When the number of rotations of the rear motor decreases, the coil may be temporarily switched to the number of coils at the time of start-up and driven to the steady rotation number, and when the number of steady rotations is reached again, the number of coils at the steady rotation may be changed.

[0030]

As described above, according to the present invention, a current is supplied to a predetermined number of coils when the motor is started, and a current is supplied to a smaller number of coils than the predetermined number when the motor is in steady rotation. Since the motor is driven, the noise level can be constantly reduced from the start of the motor to the steady rotation.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of a brushless motor according to an embodiment of the present invention.

FIG. 2 is a block diagram showing a motor drive circuit of the present embodiment.

FIG. 3 is a diagram showing an output waveform of each signal at the time of starting the motor of the present embodiment.

FIG. 4 is a diagram illustrating a state of a current flowing through a coil when the motor of this embodiment is started.

FIG. 5 is a diagram showing an output waveform of each signal during steady rotation of the motor of the present embodiment.

FIG. 6 is a diagram illustrating a state of a current flowing through a coil during steady rotation of the motor according to the present embodiment.

[Explanation of symbols]

 1 Main Magnet Section 2 FG Magnet Section 3 FG Pattern 5 Zero Cross Detector 6 Phase Comparison Circuit 7 External Clock 9 Position Detection Signal Processing Circuit 10 Hall Amplifier 13 Amplitude Processing Circuit 14 Current Driver 15 Error Amplifier A Coil Section M Magnet Section O Rotation Axis C1 ~ C6 Coil H1 ~ H3 Hall element

Claims (1)

[Claims] 1. A brushless motor in which current is supplied to a plurality of coils and a magnet is rotated by a magnetic field generated in each coil, the current is supplied to a predetermined number of coils at the time of starting the motor, and when the motor is in a steady rotation. A brushless motor comprising drive means for supplying current to a number of coils smaller than the predetermined number.